In a conventional railway truck of the four-wheel type, the truck geometry is such that the axles are constrained by the bearings and sideframes to remain substantially parallel to each other under all conditions of operations. Generally, a ninety degree relationship is desired between the wheelsets and the sideframes during travel on straight track, while limited and restrained relative turning is permitted between the wheelsets and sideframes when the trucks travel along curved tracks.
If there are small differences in the longitudinal dimensions of the sideframe pair wheelbases or if there is longitudinal movement between the bearing adapter assembly and the pedestal jaws, wheel misalignment will be created, along with excess drag. These conditions will also open the opportunity for truck hunting to occur. Surprisingly, this means that drag can occur even on straight track. Under these conditions, a substantial amount of dragging and scraping of the wheels will occur, thereby wasting a great deal of locomotive horsepower and fuel in overcoming the friction forces associated with wheel misalignment.
To restrain the drag associated with wheel misalignment, prior art structures have interposed elastomeric devices between the bearing adapters and the sideframes for maintaining the wheelsets and sideframes in a generally right angular relationship to each other while traveling on straight track. These devices were said to significantly reduce truck misalignment and associated drag. Typical structures of these prior art devices are shown in U.S. Pat. Nos. 4,674,412, 3,638,582 and 3,276,395, that typically comprise an elastomeric pad sandwiched between a pair of plates. They are located between the bearing adapter and the roof of the pedestal jaw, and they require machining to install, but once installed, they accurately locate the bearing adapter between an opposed pair of machined thrust lugs on each pedestal jaw wall. However, it has been discovered that the as-cast pedestal jaw wall area near the axle centerline, even when cast to proper manufacturing tolerances, can limit wheel bearing displacement necessary for designed axle steering and radial alignment. Moreover, it has also been discovered that the same as-cast walls can be a major contributor to the cause of curving drag. Curving drag is considered herein to be the drag caused by the failure of the truck, for whatever reason, to permit the wheel sets to assume a radial orientation.